The present invention relates to improvements in electrical switching apparatus such as is used in controlling warning lights aboard school buses and the like, and, in one particular aspect, to novel and improved switching arrangements for operator-selected control over certain automatic door-actuated excitations of warning lights, as well as to unique momentary-interrupting switch constructions which are especially suited to the requirements of such switching arrangements.
A conventional attention-commanding safety warning-light system for school buses involves the flashing of amber warning lights as the vehicle approaches a stop, and then the flashing of red stop lights so long as the door or doors are open to permit the boarding or discharge of passengers. Preferably, such a system is under control of a door-operated switch which will insure that the stop lights must operate without fail during those hazardous times when passengers may be alighting or entering. However, it is also mandatory that the same vehicle not display flashing stop lights when at rest for other purposes, such as a temporary halt with door open as required by law at a railroad crossing. These conflicting requirements can be satisfied in part by way of a simple type of operator-actuated switching which would disable the warning system, but this introduces another control and device to which an already busy operator must give attention, and there is no assurance that the warning system will always be reset to function when needed. More complex networks, involving additional door-operated switches, for example, tend to introduce significantly higher costs, both as to system components and installation.
In accordance with certain aspects of the present teachings, the creation of a relatively simple and inexpensive warning-light system for school buses, involving only a single door-operated switch unit, which will reliably condition itself for single-cycle automatic sequencing of both flashing warning and stop lights upon actuation by the operator, is linked to the concept of having the door switch momentarily interrupt one of its switching circuits only when the door is being closed after having been opened. That momentary interruption is effective to reset a self-holding solenoid switch by which the operator had initiated one cycle of sequencing of the flashing lights, and, thereafter, the operator may intentionally omit the sequencing by refraining from actuation of the solenoid switch when the bus is to stop for some purpose other than admitting or discharging passengers. Once the system has been operator-conditioned to follow the desired sequencing, however, it will be strictly observed in accordance with door opening and closure, without further operator attention.
The momentary-interrupt switching entailed in the foregoing is unusual in that a single door-actuated plunger must be capable of simply shifting electrical excitation from warning to stop lights during a movement in one direction associated with the opening of the door, and, during its movement in the opposite direction, associated with closing of the door, it must momentarily break another circuit which is nevertheless not interrupted by the other movement.